Arylene sulfide polymer coating compositions

ABSTRACT

ADHERENT COATINGS OF ARYLENE SULFIDE POLYMERS ARE FORMED BY APPLYING TO SUBSTRATES A MIXTURE OF ANY ARYLENE SULFIDE POLYMER AND SELECTED NITROGENOUS ORGANIC COMPOUNDS. THE ACRYLENE SULFIDE POLYMER-NITROGEN-CONTAINING ORGANIC COMPOUND MIXTURE IS PREFERABLY APPLIED AS A SLURRY TO A SUBSTRATE IN A CARRIER LIQUID, SUCH AS ETHYLENE GLYCOL, METHYL ALCOHOL, WATER, TOLUENE, AND THE LIKE OR MIXTURES THEREOF, AND THEREAFTER HEATED TO FORM A COATING.

United States Patent 3,776,880 ARYLENE SULFIDE POLYMER COATING COMPOSITIONS Jennings P. Blackwell, Bartlesville, Okla., assignor to Phillips Petroleum Company No Drawing. Filed Sept. 1, 1971, Ser. No. 177,130 Int. Cl. C08g 51/04 US. Cl. 260-37 R Claims ABSTRACT OF THE DISCLOSURE This invention relates to improved arylene sulfide polymer coatings. In accordance with another aspect, this invention relates to normally solid arylene sulfide polymer coating compositions containing selected nitrogenous organic compounds. In accordance with a further aspect, this invention relates to improved phenylene sulfide polymer coatings containing at least one nitrogenous organic compound applied as a slurry in a carrier liquid to a metal substrate and heated at an elevated temperature and for a period of time sufficient to fuse and cure said polymer.

Arylene sulfide polymers such as phenylene sulfide polymers are well known in the art for their temperature stability. Although it is known in the art that these polymers can be adhered to metal substrates, under certain conditions there sometimes are formed microscopic voids between the substrate and the polymer coating and surface imperfections which cannot necessarily be detected by ordinary means, but which have an effect on the ultimate value of the coated article as an item of commerce. For instance, a coated metallic item on which the coating is stuck tenaciously throughout most of the interface is still unsuitable as a protective coating for certain uses if there are microscopic areas where the protective coating is not intimately adhered, thus forming points for separation of the coating and the initiation of corrosion. Furthermore, in applications such as nonstick coatings for cooking utensils for which phenylene sulfide polymers and the like should be ideally suited because of their temperature stability and exceptional hardness, a surface is desirable which is not only glossy to the appearance but which does not even contain microscopic voids or surface imperfections.

It has been the subject of considerable research to find methods of improving the bonding of coatings of arylene sulfide polymers to substrates which are to be protected. One of these methods which has been highly successful has involved the incorporation of titanium dioxide into the coating composition.

I have now found that even 'better coatings of arylene sulfide polymers can be formed by incorporating into the coating a nitrogenous organic compound. Coating containing these materials can also contain titanium dioxide to provide even superior coatings.

It is an object of this invention to provide an improved coating to an arylene sulfide polymer.

Another object of this invention is to provide an improved method of applying coatings of arylene sulfide polymers to substrates.

A further object of this invention is to provide an improved high temperature coating composition.

Patented Dec. 4, 1973 A further object of this invention is to provide a coating free of microscopic imperfections which coating is uniformly adhered to a substrate.

In accordance with this invention, a minor amount of at least one nitrogenous organic compound is incorporated into an arylene sulfide polymer and this mixture is applied as a coating to a substrate.

Further in accordance with the invention, a metal substrate is coated with a slurry comprising an arylene sulfide polymer and a finite amount up to 50 weight percent, based on polymer, of at least one nitrogenous organic compound, followed by heating at an elevated temperature for a period of time suflicient to fuse and cure the arylene sulfide polymer.

It has been found that the addition of at least one nitrogenous organic compound, as defined herein, to arylene sulfide polymer coating compositions results in coatings having improved adhesion or smoothness upon fusion and curing.

Specific nitrogenous organic compounds effective in improving the adhesion or smoothness of coatings comprising arylene sulfide polymers include melamine, hexamethylenetetramine, benzothiazole, lH-benzotriazole, or casein or ammonium salt of casein. Mixtures of these nitrogenous compounds can be employed.

Applicable arylene sulfide polymers include polymers of the type which are prepared as described in US. 3,354,129. As disclosed in this patent, these polymers can be prepared by reacting a polyhalo-substituted cylic compound containing unsaturation between adjacent ring atoms and an alkali metal sulfide in a polar organic compound. The resulting polymer contains the cyclic structure of the polyhalo-substituted compound coupled in repeating units through a sulfur atom. The polymers which are preferred for use in the coating procedure of this invention, because of their high thermal stability and availability of the materials from which they are prepared, are those polymers having the repeating unit -R-S-- where R is phenylene, biphenylene, naphthylene, biphenyl ether, or a lower alkyl-substituted derivative thereof. By lower alkyl is meant alkyl groups having 1 to 6 carbon atoms such as methyl, ethyl, propyl, isobutyl, hexyl, and the like. Preferably the arylene sulfide polymers have melting temperatures within the range of about 400-900 F. If desired, the arylene sulfide polymer can be lightly cured, i.e., the molecular weight of the polymer can be increased by cross-linking or chain extension, e.g., by heating moderately, prior to application to the substrate.

With the exception of benzothiazole, the nitrogenous compound should 'be employed in an amount of about 2-50, preferably 340, parts by weight per parts of arylene sulfide polymer. To achieve satisfactory results benzothiazole, when used, should be employed in an amount of at least 15 parts by weight per 100 parts of arylene sulfide polymer.

The diluent or carrier liquid used as a component of the slurry can be any liquid inert to the other components of the slurry and to the substrate, provided it can be readily volatilized prior to or during the subsequent heating or curing step. The diluent presently preferred is Water. Other diluents which can be used include alcohols such as ethylene glycol, methyl alcohol, ethyl alcohol, and isopropyl alcohol, and hydrocarbons such as benzene, toluene, heptane, cyclohexane, and various hydrocarbon mixtures such as kerosene, diesel fuel, and the like. Mixtures of such diluents can be employed.

The concentration of the polymer in the diluent depends upon the coating application and whether or not additional solids, besides the nitrogenous compound, are employed. As a practical matter, the slurry should not be so dilute that the polymer particles are not closely enough associated on deposit on the surface to permit them to fuse together on melting. On the other hand, the thickness of the slurry and its ease of application will impose a practical upper limit on the solids concentration. Generally a solids content of about 10-60 weight percent can be used. In addition to the arylene sulfide polymer and which have been molded, carved, or otherwise formed into specific shapes, and the like.

EXAMPLE In each of a series of experiments, a metal coupon was the nitrogenous compound, other substances can be in- 5 coated with an aqueous slurry comprising 100 parts by corporated into the slurry, such as other polymers, e.g., weight of poly(p-phenylene sulfide) (PPS) in 225-300 poly(tetrafluoroethylene); pigments, e.g., titanium diparts by weight of water contaming 1 weight percent oxide, ferric oxide, cobaltic oxide, or molybdenum disul- Triton X-100 surface active agent. vEach slurry was prefide; fillers; surfactants; and the like. pared by ball milling these ingredients, together with any The slurry can be applied to the substrate without prior other component such as nitrogenous compound within heat treatment of the substrate, or the substrate can be the scope of this lnvention, pigment, or poly(tetrafluoroheated prior to or during application of the slurry to temethylene) for 6-18 hours. The coated coupon was heated peratures as high as 600-800 F. at 700 F. for 30 minutes to cure the arylene sulfide Any surface that can be heated to the coating temperacoating, i.e., increase the molecular weight of the arylene ture necessary to fuse the arylene sulfide polymer can be sulfide by crosslinking and/or chain extension, after coated by the procedure of this invention. In general, the which the coating was evaluated. In runs 1-25 the metal articles which are coated are those in which the surfaces coupon was copper; in runs 26-27 the metal coupon was are formed of thermally stable polymeric materials or aluminum. The runs and observations made are sumsubstances such as metal, glass, ceramic, or stone. Prefcrmarized in the following table.

TABLE Cured coating Additive (parts by weight/100 parts PPS) Thick- Reverse ness, impact Run Pigment Nitrogenous compound mils Appearance Bend test test Number:

1 TiOz (33) Melamine (10) 5 Good, smooth No cracks..- No cracks.

3) Non 5 Mottled, incomeplete coverage Cracks Crac s T102 (25) Melamine (7 5).. 4 Good No cracks.-- No cracks.

101(25) None 5 Poor cov (racks racks. 102 (33 Melamine (l7). 4 Good, smooth No cracks. No cracks. s T10, (33)-. Melamine (24)-.- 4 d d D0. 7 TlOz (33) Melamine (33)... 4 Do. 8 a TiOz 33)- Melamine (l0). 5 Do 9 TiOz (3 -.do 7 D0. 10..-" a 5 Do. 11-- Cracks. 12 No cracks... No cracks. 13 do Do. 14".... 4 do- Do. 15 -do. -do 7 .-..do .do--- Do. 16 TiOz (33).. None 4 Veryt poor, with many pinholes and Cracks Cracks.

0T3 ers. 17 'IiOz (33) Melamine (l0) 4% Smooth, glossy No cracks... No cracks. 18 'IiOz (33) Casein (10)... 4 Even, flat, dark. do Do, is TiO: (as) Casein (a) 4 Smooth, dark.. Do. 20 TiOi (33) Hexamethylenetetramine (l0) 5 Mottled Do. 21 TiOz (33) Hcxamcthylenctetramine (33) Good, but with some small dent Do. 22 None Hexamethylenetetramine (13)-. Dark, smooth, glossy Do. 23- -.do. Hexamethylenetetramine (33) Dark and glossy, a few bare spo Do. 24 TiOz (33) Benzothiazole (33 Incomplete coverage Do. 25 T102 (33). lH-benzotriazole (10) 3% goontvlillith pipllliples and (graterth 1:60. 26 T102 (33)- Melamine (10) 2% s i iiiilai i niulafi i tis i hz absence of U o- 27 102 Oasem nitrogenous compound I Mandrel bend test. The coupon is bent to a 90 angle, and the resulting cured surface is examined for cracks.

b Gardner laboratories reverse impact test. The equipment used comprises a rounded tip which rests above the sample on the reverse side from the coating. A 4-pound ram is raised inches and dropped against the tip, which them impinges on the back side of the coated coupon. The side opposite that which comes in contact with the tip, i.e.hthe side having the coating, is examined for cracks and looseness of the coating.

e Formulation was applied as two coats, eac d Not determined.

cured 30 minutes at 700 F.

I PPS was heated for about 6 hours at approximately 500 F. prior to preparation of slurry.

l Sutlicient ammonium hydroxide was added to dissolve the casein.

ably, metals such as copper, aluminum, iron, titanium, and chromium or metal alloys such as steel are used.

After the coating is applied, it is desirable to cure the coating, i.e., increase the molecular weight of the arylene sulfide polymer by crosslinking or chain extension, by heating at an elevated temperature, preferably in the range of about SOD-900 F., in an oxygen-containing atmosphere, such as air, for about 5 minutes to 24 hours or more. The thickness of the coating can be increased by additional applications following the same procedure after each curing period. The slurry can be applied by any procedure such as by spraying the slurry onto the surface or by flowing the slurry over the surface.

In order to obtain the improved coatings provided by the process of this invention, the thickness of the cured coating should be at least 2 mils and can be as much as mils or more, with the proviso that when copper is used as the substrate, the thickness of the cured coating should be at least 3 /2 mils.

To produce the coated or laminated structure, the substrate as used in the present invention can be in any shape desired, including sheeting, wire, coupons, blanks, objects As the above table indicates, the presence of a nitrogenous compound, as shown, in the slurry applied to the substrate results in a coating which, upon curing, exhibits improved adhesion and/0r smoothness as compared with a coating prepared similarly from a slurry containing no nitrogenous compound.

I claim:

1. A coating composition comprising a poly(arylene sulfide) resin and about 2 to 50 weight percent, based on resin, of at least one nitrogenous organic compound selected from the group consisting of melamine, hexamethylenetetramine, benzothiazole, lH-benzotriazole, casein, and an ammonium salt of casein, and mixtures thereof.

2. The coating composition of claim 1 which is poly- (phenylene sulfide), melamine and a minor amount of tianium dioxide or ferric oxide.

3. The coating composition of claim 1 which is polyphenylene sulfide), hexamethylene tetramine and a minor amount of titanium dioxide and poly(tetrafiuoroethylene).

4. A composition according to claim 1 wherein said resin is poly(phenylene sulfide) and the amount of said nitrogenous organic compound present is from about 3 3,524,835 8/1970 Edmonds et a1 260-79 X to 40 weight percent. 3,290,299 12/1966 Kumins et a1. 260--37 RX 5. A composition according to claim 4 which contains 3,366,623 1/1968 Ronco 260-37 RX in addition a minor amount of titanium dioxide or ferric 3,622,376 11/ 1971 Tieszen et a1. 260-79 UX oxide and p01y(tetrafiuoroethy1ene). 5

LEWIS T. JACOBS, Primary Examiner References Cited UNITED STATES PATENTS US. Cl. X.R.

3,303,170 2/1967 Pike 26037 RX 79 3,699,087 10/1972 Wood et al. 26079 10 

